1. Field of the Invention
This invention relates to mechanisms for lifting sheet material, and in particular relates to a lifting mechanism especially designed for handling oversized, metal panels or plates which are to be moved to and from upright storage bins.
2. Description of the Prior Art
Mechanisms for handling sheet materials such as large metal plates are well known. U.S. Pat. No. 3,976,321 assigned to the assignee hereof and entitled "Sheet Material Handling Apparatus", and my U.S. Pat. No. 4,181,341 entitled "Apparatus for Lifting Sheet Material", for instance, disclose mechanisms suitable for handling standard-sized metal sheet materials. Those skilled in the art will realize that sheet materials are most advantageously stacked in an upright orientation, and as such the beforementioned lifting mechanisms disclose upper and lower grippers, in the form of hooks, for engaging the upper and lower marginal ends of the panel to be lifted. It is a feature of such lifting mechanisms that the lower gripper member or hook is provided with means for engaging and disengaging the lower hook from the lower marginal end of the lifted panel or panels in order to provide for selective engagement and disengagement of the lifting mechanisms with a panel. The mechanism for engaging and disengaging the lower hook must have the capability of remote control, since it is generally not safe for an operator to place himself between upright panels.
U.S. Pat. No. 3,976,321, for example, discloses a lifting mechanism provided with relatively complicated and therefore somewhat expensive mechanism for relatively swinging the lower gripping hooks of the lifting mechanism into and out of positions for engaging and disengaging the lower marginal end of a vertically stacked, sheet-like plate or panel. U.S. Pat. No. 4,181,341 also discloses a less costly, more trouble free lifting mechanism wherein the lower gripping hooks have initially sheet clearing cocked positions such that upon release they are capable of pivoting into a position wherein they are disposed for engaging the lower marginal end of a lifted panel. The lifting mechanism of the U.S. Pat. No. 4,181,341, with its pivotal lower hooks, has proven to be an excellent, cost-effective tool for the lifting of standard sized metal plates or panels. Lifting mechanism having pivotal lower hooks as taught in the U.S. Pat. No. 4,181,341, however, is limited to some extent in its load capacity, since it is axiomatic that some of the structural integrity of a hook must be sacrificed in order to provide for the hook to have the ability to be pivotally shifted.
There are instances wherein oversized, heavy sheet metal panels or plates each weighing up to 15,000 pounds or more are required to be lifted and transported. The unit for lifting and moving the sheets, either singly or in multiple, must be capable of handling horizontal as well as upright sheets with equal facility, even if the upright sheets are in closely adjacent stacks. A lifting mechanism which has the ability to be engaged and disengaged by remote control from generally vertically oriented metal plates, but which at the same time has a lower gripping hook that requires no pivoting parts inherently has a decided advantage in handling such oversized, heavy plates.